HAMPSHIRE FLORA GROUP GRASSES WORKSHOP Workshop Notes 17th July 2010 Martin Rand Contents Introduction.............................................................................................. 3 Grass Structure and Features..................................................................... 5 Roots and Shoots................................................................................... 5 Stems, Leaves and Tillers ....................................................................... 5 Inflorescence......................................................................................... 6 Spikelets, Flowers and Seeds.................................................................. 7 A Note on Finer Anatomy ....................................................................... 8 Measurements ....................................................................................... 8 Distinguishing Grasses from Other Monocots ........................................... 8 Classification: Tribes and Genera...............................................................10 Oryzeae (Rice-grasses)..........................................................................10 Nardeae (Mat-grass) .............................................................................10 Stipaeae...............................................................................................11 Poeae...................................................................................................11 Hainardieae (Hard-grasses) ...................................................................12 Aveneae...............................................................................................12 Meliceae...............................................................................................16 Brachypodieae (False-bromes)...............................................................17 Bromeae (Bromes)................................................................................17 Triticeae...............................................................................................17 Arundineae...........................................................................................18 Eragrostideae .......................................................................................19 Cynodonteae ........................................................................................19 Paniceae ..............................................................................................20 Andropogoneae ....................................................................................21 Key Genera..............................................................................................22 Oat-grasses: Helictotrichon, Arrhenatherum, Avena, Trisetum .................22 Meadow-grasses and Saltmarsh-grasses: Poa and Puccinellia ..................22 Fescues and Rye-grasses: Festuca, Lolium and Vulpia.............................23 Bents: Agrostis .....................................................................................24 Bromes: Bromus ...................................................................................25 Resources................................................................................................28 Further Reading....................................................................................28 Useful Equipment..................................................................................29 Acknowledgements ..................................................................................31 2 Introduction It is hard to over-estimate the importance of grasses to life on earth in the present era. Having (as far as we can tell) evolved in the early Tertiary, 55-65 million years ago, they rose to dominate about a third of Earth’s land surface by natural means, while through agriculture our own dependence on them for life has become critical. The total number of species in the grass family Poaceae is large (about 10,000), ranking it probably fifth in the family league table. Generally it is considered to have three evolutionary lines, comprising a number of subfamilies: .Bambusoideae (Bamboos and Rice-grasses): while hugely important world-wide they are mostly tropical species, and we shall not devote much attention to them in this workshop. However an increasing number of species is becoming established in the wild in Britain. .Arundinoideae, Chloridoideae, Panicoideae. etc: a diverse set of subfamilies, mostly tropical and southern hemisphere, that includes just a few important native genera in Britain such as Phragmites (Common Reed), Molinia (Purple Moor-grass), Danthonia (Heath-grass) and Spartina (Cord-grass). However the Panicoideae in particular includes several non-native species that are increasingly frequent in Britain. .Pooideae: temperate plants, including most of our native species. Although the taxonomy of grasses was originally worked out on the basis of visible characters such as spikelet structure, and while this approach still works well for constructing artificial keys, it hides many details of parallel or convergent evolution – grasses have succeeded by playing endless variations on a relatively small repertoire of structural features. The natural relationships of grasses are now described on a much wider set of criteria including detailed anatomy, cytology, photosynthetic metabolism and genetics. Anyone interested in more background, and in gaining an appreciation of grasses on the world stage, is recommended to read Clayton & Renvoize (1986). Understanding a little of grass classification is important because the new standard handbook for British grasses, and the basis for this course, Cope & Gray (2009), uses a hierarchical key system that identifies first to tribe, then to genus, then to species. (From now on we refer to this as ‘the Handbook’.) This is the approach adopted on a world scale by Clayton and Renvoize. Anyone who has used the earlier major British field guide, Hubbard (1954, 1968, 1981) will know that the identification key takes one directly down to species. This has the advantage that it can be as ‘artificial’ as one likes, picking only the best field characters; but it can make for very long and tedious pathways through the key. With the inclusion of many more non-native species such an approach would probably have been unworkable. Most other technical floras key to genus in the first place, or to an artificial grouping of genera where different members of the same genus are arrived at through different groupings. The subfamilies mentioned above are subdivided into Tribes. There are 40 of these worldwide, but you will be relieved to know that in Britain there are only 15, and 7 of these either consist only of relatively casual introductions, or comprise one or a few easily recognisable genera. The tribes can be distinguished on field characters, and it is a feature of the Handbook that all distinguishing characters described are observable in the field and without the need for dissection. However fine measurement is sometimes needed. With a little practice and experience, you will be able to place most grasses in the correct genus without the need for the top levels of key, and to run an unfamiliar species down to its correct genus using the features given. The Handbook provides a great deal of information on grass structure and features, biology and ecology, as well as keys and useful identification hints. It is not our intention to repeat these here, 3 and the following notes will simply offer comments or point out things that may otherwise be missed in the wealth of detail. Finally, it may come as a further relief that Tom Cope is temperamentally a ‘lumper’, based on his knowledge of variation in a species outside one narrow geographical range, as well as the practical consideration that if a feature cannot be readily observed then it is of little or no use to most of the potential Handbook users. However he does describe variation within species where it is readily observable, and deals comprehensively with ‘awkward’ genera such as Festuca and Bromus. Unlike Hubbard, the Handbook’s illustrations concentrate on distinctive features rather than illustrating every part of the plant. The Handbook gives much fuller coverage to alien species than Hubbard, in both numbers of taxa and level of detail. With several species becoming more common and more persistent, this is very desirable. 4 Grass Structure and Features Features of the grass plant are described on pages 10-19 of the Handbook. It is worth taking to heart Cope’s statement on p. 10 that “grasses... have a tendency to be relaxed about the finer distinctions between annual and perennial”. This is something to watch out for in genera like Poa (Meadow- grasses) and Bromus (Bromes) particularly. Look at the more mature plants where possible and be prepared to reserve judgement. Roots and Shoots With a few notorious exceptions like Ammophila (Marram), grass roots tend to be fine and matted, and to penetrate to no great depth. Fortunately both for us and for the grasses, the roots hold few useful recognition characters. Much more important is the system of stem branching close to the ground that enables many perennial grasses to maintain their lifestyle and to spread, regardless of grazers, mowers and other contingencies of life. These branches, with new growth buds, may be short and relatively crowded in tussock-forming species; or they may form runners at or just above ground level (stolons);